Single phase brushless DC motor has been developed rapidly in recent years, and the structure is generally winding the stator windings on the stator core, which creates a changing magnetic field after powered on, so as to drive the rotors embedded with permanent magnet rotation. As the stator core needs to be wound with stator windings, therefore, slots are usually provided on the stator core for proceeding the process of automatic winding.
However, the existence of the slots increase the magnetic resistance between the part of the stator core where the slot is defined and the rotor permanent magnet, the stator core has starting dead point. That is to say that the magnetic pole axis of the rotor automatically deflects towards a direction in which the magnetic resistance is small when the motor is in a non-energized state or has no significant rotation block, that is, the magnetic pole axis of the rotor deviates from the axial direction of the slots. At this point, the rotor is subjected to zero torque, resulting in motor starting instability.